In an LTE system, as a connected state of user equipment UE (which is referred to as a “UE,” hereinafter) with a base station eNB (which is referred to as an “eNB,” hereinafter), there are two states, that is, a radio resource control (RRC) idle state (RRC Idle) and an RRC connected state (RRC_Connected).
When the UE is connected to a network, a UE context is generated by a mobility management entity (MME) on a core NW side, and in the RRC connected state, the UE context is retained in a UE and an eNB, to which the UE is connected. The UE context is information including bearer-related information, security-related information, etc.
When the UE performs transition between the RRC idle state and the RRC connected state, signaling of call control including that of the core NW side frequently occurs, so that the problem is how to reduce the signaling.
For example, when the UE transitions from the RRC connected state to the RRC idle state, signaling illustrated in FIG. 1 occurs (e.g., Non-Patent Document 1). The case of FIG. 1 is a case in which an eNB 2 detects that communication of a UE 1 is not performed for a predetermined time, disconnects a connection with the UE 1, and transitions to the RRC idle state.
In FIG. 1, the eNB 2 transmits a UE context release request to an MME 3 (step 1). The MME 3 transmits a bearer release request (Release Access Bearers Request) to a serving gateway (S-GW 4) (step 2), and the S-GW 4 transmits a bearer release response (Release Access Bearers Response) to the MME 3 (step 3).
The MME 3 transmits a UE context release command to the eNB 2 (step 4). The eNB 2 transmits an RRC connection release to the UE 1 (step 5) so as to cause the UE 1 to release the UE context to transition to the RRC idle state. Further, the eNB 2 releases the UE context and transmits a UE context release complete to the MME 3 (step 6).